1. Field of the Invention
The present invention relates to a paper folding mechanism used for e.g. an electrophotographic printer. More specifically, it relates to a paper folding mechanism for alternately folding continuous recording paper to be stacked in a paper stacker disposed at the end of the paper transfer path of a printer.
2. Description of the Related Art
Conventionally, various kinds of paper folding mechanisms have been used for electrophotographic printers. FIG. 12 of the accompanying drawings shows an example of conventional folding mechanisms.
Specifically, the illustrated conventional paper folding mechanism 200 includes a swing guide 1, a plurality of first paper guides 102a and a plurality of second paper guides 102b. The swing guide 1, supported by a driving shaft 14, is caused to swing between the first and the second paper guides 102a, 102b. The paper guides 102a and 102b are fixed, at their upper ends, to a first frame 110a and a second frame 110b, respectively, to be held in an upright position. The first paper guides 102a are spaced from the counterpart second paper guides 102b by a distance equal to the xe2x80x9csheet lengthxe2x80x9d (defined below) of continuous paper.
Referring to FIG. 11, a typical example of continuous recording paper is shown, which is equally usable for the conventional folding device and a device of the present invention. The illustrated paper P is formed with a series of indexing holes P1 disposed at regular intervals along each longitudinal edge Pa and Pb. Further, the paper P is provided with a plurality of fold lines (perforation lines) P2 each of which extends across the paper P. These perforation lines P2 are spaced from each other longitudinally of the paper P by a constant pitch or xe2x80x9csheet lengthxe2x80x9d L. The continuous paper P can be readily severed into separate paper sheets due to the perforation lines P2. Different types of continuous paper may have a different width W and/or sheet length L.
The conventional paper folding mechanism 200 further includes a vertically movable stacker table T, a plurality of first rotary blades 103a and a plurality of second rotary blades 103b. The printed recording paper, after being folded by the first or second blades, is piled on the stacker table T. The first rotary blades 103a are attached to a first driving shaft 104a and arranged adjacent to the first paper guides 102a, while the second rotary blades 103b are attached to a second driving shaft 104b and arranged adjacent to the second paper guides 103b. The first driving shaft 104a is rotatably attached to the first frame 110a, while the second driving shaft 104b is rotatably attached to the second frame 110b. 
As shown by the two-headed arrow Ar in FIG. 12, the first frame 110a is movable toward or away from the second frame 110b, whereby the first paper guides 102a, which are carried by the fist frame 110a, can be moved closer to or farther away from the counterpart second paper guides 102b. Such an adjustable guide distance between the first and the second paper guides is advantageous to dealing with various types of continuous paper having different sheet lengths L.
In operation, the swing guide 1 is caused to swing about the axis of the shaft 14. In synchronism with this swing motion, a predetermined length of the paper P will be paid out from the guide 1. Thus, the paid-out portion of the paper P will be warped near the first paper guides 102a or second paper guides 102b (see FIG. 13). Then, with the paper P being thus warped, the first rotary blades 103a or second rotary blades 103b will hit upon the warped paper portion, thereby folding the paper P along the perforation line P2. As the volume of the paper P stacked on the stacker table T increases, the table T is lowered, so that the first and the second rotary blades 103a, 103b can hit the paper P properly for folding the paper.
In the conventional paper folding mechanism, as stated above, the first paper guides 102a and the first driving shaft 104a are attached to the same movable frame 110a. Thus, the positional relation between the guides 102a and the shaft 104a will remain the same before and after the first frame 110a is moved in the directions of arrow Ar. This unchanging positional relation renders the conventional paper folding mechanism disadvantageous in the following points.
For clarifying the problem of the conventional paper folding mechanism, it is now supposed that use is made of continuous paper having a relatively long sheet length L. In this case, as shown in FIG. 13, the distance between the first and the second paper guides 102a, 102b will be increased in accordance with the sheet length L, to accommodate the folded paper. Also, a relatively great length of paper is paid out from the swing guide 1 for performing one paper-folding operation by the first or second rotary blades.
In such an instance, as shown in FIG. 13, the paid-out paper P tends to be warped with a rather great radius of curvature. As a result, the warped portion of the paper P may fail to come close enough to the rotary blades 103a, so that the warped portion will merely be pushed toward the second paper guides 102b by the blades 103a without being folded at all.
Another example of erroneous paper-folding in the conventional mechanism is shown in FIG. 14. Specifically, being partially folded, the paper P may suffer from a wrinkle N generated at a fold line P2. Such a defect may often be observed when solid printing is performed across the perforation line P2, since the solid printing portion tends to prevent the paper P from being properly folded.
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a paper folding mechanism designed to overcome the above conventional problems.
According to the present invention, there is provided a paper folding mechanism for continuous paper provided with fold lines spaced by a constant sheet length. The folding mechanism includes: a swing guide caused to pivot for guiding the paper; a first and a second paper guides spaced from each other by a guide distance corresponding to the sheet length, the first paper guide being displaceable relative to the second paper guide; and a paper presser arranged adjacent to the first paper guide for folding the paper along the fold lines. The paper presser is displaceable relative to the first paper guide.
With such an arrangement, it is possible to move the paper presser closer to or away from the continuous paper to be folded. Thus, by adjusting the position of the paper presser, a warped portion of the paper will be properly hit by the paper presser, which is advantageous to folding the paper properly.
In a preferred embodiment of the present invention, the paper presser may include a presser blade and a rotatable shaft to fix the presser blade. In this case, the shaft is displaceable relative to the first paper guide.
Preferably, the presser blade may include a free end portion and a base end portion fixed to the rotatable shaft, wherein the free end portion is more flexible than the base end portion. With such an arrangement, the paper is effectively prevented from being torn by the presser blade.
Preferably, the paper folding mechanism of the present invention may further include paper presser shifting means for displacing the paper presser relative to the first paper guide in accordance with displacement of the first paper guide. With such an arrangement, the paper presser can be automatically moved relative to the first paper guide. For instance, the paper presser shifting means may cause the paper presser to approach the first paper guide as the guide distance becomes greater.
Preferably, the paper presser shifting means may include a side plate for rotatably fixing the shaft, a lever pivotable relative to the side plate, a guide rail with which the lever is held in slidable contact, and a paper guide supporting member to which the first paper guide is attached. The paper guide supporting member is engaged with the lever and displaceable relative to the side plate.
Preferably, the guide rail may be provided with an inclined edge, and the lever may be provided with a roller urged into contact with the inclined edge of the guide rail.
According to the present invention, the paper folding mechanism may further include presser blade halting means for retaining the presser blade in a home position before the presser blade hits the paper. In the home position, the presser blade may be inclined toward the paper beyond the first paper guide. With such an arrangement, the warping of the paper will be prevented from becoming unacceptably large. Thus, the presser blade can properly fold the paper along the fold lines.
Preferably, the presser blade halting means may include a sensor for detecting a rotational position of the shaft. Further, the presser blade halting means may include a home position detection plate attached to an end of the shaft.
In the above case, the sensor may be provided with a light emitting portion and a light receiving portion spaced from the light emitting portion. When the shaft is rotated, the home position detection plate may be periodically brought into a clearance between the light emitting portion and the light receiving portion when the shaft is rotated. As a result, the light emitted from the light emitting portion is shielded by the detection plate, whereby it is known that the presser blade has been brought to the home position.
According to a preferred embodiment of the present invention, each of the paper guides may be provided with an inclined upper portion and an upright lower portion, wherein the upper portion is inclined to extend along the paper to be folded.
Preferably, the inclined upper portion may be connected to the upright lower portion by a hinged portion permitting adjustment of an angle between the upper portion and the lower portion.
Preferably, the paper folding mechanism of the present invention may further include auxiliary paper folding means attached to the swing guide. The auxiliary paper folding means may be a chain dangling from the swing guide.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.